The present invention relates generally to a multi-phase DC-to-DC buck converter, and more particularly, to an apparatus and method for multi-phase current balance and adjustable load regulation for a multi-phase DC-to-DC buck converter.
The multi-phase DC-to-DC buck converter has been widely used for power supply circuits. In a multi-phase DC-to-DC buck converter, there are several pairs of switches of which each pair of switches is controlled by a respective pulse width modulation (PWM) signal with phase shift but generate a single output voltage, i.e., the converter output voltage. Unfortunately, there may be current unbalance occurred between the different phases or channels thereof due to the mismatching of parameters in the multi-phase DC-to-DC buck converter. For multi-phase current balance, a prior art converter disclosed by U.S. Pat. No. 6,278,263 issued to Walters et al. equally shares the load current between each of the phases or channels in the converter by averaging all of the channel currents with summing circuit and scaling circuit for balance control between the channels in addition to the comparison of the converter output voltage with a reference voltage to generate each PWM signal for the respective channel. However, this prior art circuit regulates each PWM signal by combining the differential voltage, between the converter output voltage and a reference voltage with the differential current between the corresponding channel current and the average channel current to generate the feedback control signal of the PWM comparator whose another input is connected with a ramp voltage to be compared with the control signal, and that makes the balance control complicated since the converter output voltage dependent control and the channel current dependent control are integrated into a control signal for the PWM comparator. Moreover, a constant reference voltage for comparison with the converter output voltage cannot be adaptive to load variations. For example, when the load of the converter changed, the droop of the converter output voltage is also changed, which degrades the performance of the converter and may result in large transient ripples. It is therefore desired improved multi-phase current balance and adjustable load regulation for a multi-phase DC-to-DC buck converter.
One object of the present invention is a multi-phase DC-to-DC buck converter with multi-phase current balance and the balance control method thereof.
Another object of the present invention is a multi-phase DC-to-DC buck converter with adjustable load regulation and the regulation control method thereof.
Yet another object of the present invention is to improve the control of the PWM signals for operating the switches of each channel in a multi-phase DC-to-DC buck converter.
In a multi-phase DC-to-DC buck converter, according to the present invention, for each channel there is a PWM comparator with two inputs for respectively receiving two control signals, one of which is derived from the feedback of the converter output voltage and the other is derived from the feedback of the corresponding channel current, and one output for producing a PWM signal for the corresponding channel. For the first feedback signal, the converter output voltage is sensed and compared with a reference signal to generate a first error signal serving as the first control signal of the PWM comparator. For the second feedback signal, the corresponding channel current is sensed and compared with the average of all the channel currents to generate a second error signal for the corresponding channel, and then the second error signal is injected into a ramp signal to either shift the DC offset of the ramp signal or increase or decrease the amplitude of the ramp signal for serving as the second control signal of the PWM comparator. This manner the excess channel current will be cut by reducing the ON-duty of the PWM comparator and the insufficient channel current will be raised by increasing the ON-duty of the PWM comparator. As a result, the unbalance between channel currents is corrected. For the adjustable load regulation, the reference signal to be compared with the converter output voltage is controlled by the summed channel current.